The invention relates to a radio signal-based positioning device and a corresponding positioning method which are suitable for use in particular in satellite navigation systems.
Global Navigation Satellite Systems (GNSS) are used for position determination and navigation on the earth and in the air. GNSS systems, such as the European Satellite Navigation System currently under construction (referred to below as “Galileo system” or “Galileo” for short), have a satellite system comprising a plurality of satellites, an earth-based receiver system connected to a central computation station, and utilization systems that evaluate and use the radio-transmitted satellite signals from the satellites.
For positioning, i.e., position determination and/or navigation, the utilization systems receive and evaluate signals from multiple satellites. The signals, in particular their propagation times, may be altered due to influence by the atmosphere. This has an adverse effect on the positioning accuracy.
Conventional positioning systems such as TRANSIT, for example, have been based on Doppler measurements. Due to the long measuring times, these positioning systems required precise modeling of the troposphere and the ionosphere. For this reason the subsequent GNSS generation has used pseudopropagation time measurements for positioning.
Since the current positioning methods use pseudopropagation time measurements for integrity of GNSS systems, such methods require precise modeling of the propagation speed in the troposphere and ionosphere.
The propagation time delays in the ionosphere may be measured with high accuracy using dual-frequency measurement. Two frequencies must be available in order to carry out dual-frequency measurements. This results in reduced continuity of service and decreased system availability.
The tropospheric component represents one error component of GNSS distance measurements which at the present time is difficult to correct. This component results from small-scale localized differences in air pressure and humidity. In the troposphere the influence of the signal propagation time is independent of the frequency, and therefore cannot be determined using a dual-frequency measurement system, as is the case in the ionosphere. The troposphere may be modeled on a global basis. However, global tropospheric models have large modeling errors. For modern GNSS systems these have become the largest error component. It is doubtful whether global tropospheric models can attain the reliability necessary for integrity systems. This reliability may be achievable for large-scale alarm barriers, but represents an unsolved problem for systems having alarm barriers in the range of 20 m.
Exemplary embodiments of the present invention provide a radio signal-based positioning device and method that provide more accurate positioning.
One aspect of the invention involves performing positioning based on the reception frequencies and send times of received radio-transmitted positioning signals. Exemplary embodiments of the present invention do not require error-prone modeling of the troposphere or dual-frequency measurements. In this manner losses in continuity and availability are avoided. As a result, the interfering characteristics of the troposphere and ionosphere no longer have to taken into account by the alarm barriers for integrity, so that the alarm barriers may be much smaller.
According to one aspect, exemplary embodiments of the present invention relate to a radio signal-based positioning device comprising
a receiver that receives a plurality of radio-transmitted positioning signals;
a frequency determiner that determines a frequency of each of the plurality of positioning signals;
a send time determiner that determines a send time of each of the plurality of positioning signals; and
an evaluation unit that determines a position location from the determined frequencies and send times of the plurality of positioning signals.
The plurality of positioning signals may be transmitted by transmitters of a global navigation satellite system. This allows the positioning device to be used, for example, as a utilization system or terminal in a GNSS system.
The frequency determiner may determine the frequency of each of the plurality of positioning signals, in each case at a reception time of the corresponding positioning signal. In this manner it is possible to detect frequency deviations which occur during the propagation time of the positioning signals.
The positioning device may also have a reference oscillator that provides a reference frequency, and the frequency determiner may determine the frequency of each of the plurality of positioning signals relative to the reference frequency. The frequency may be precisely measured using the reference oscillator.
Useful data may be transmitted via the plurality of positioning signals, and the send time determiner may determine the send time of each of the plurality of positioning signals from the useful data in the respective positioning signal.
The receiver may receive multiple positioning signals, and the evaluation unit may determine the position location from the determined multiple associated frequencies and send times. In the general case seven navigation signals are used. If a model of the earth's surface is available, only five signals are needed according to the invention. For one-dimensional motions, for example on a track, three measurements are sufficient for the invention.
The invention is further described below for the case of seven navigation signals. However, this is not intended to limit the invention to this case.
The evaluation unit may determine a position, a speed, and the reference frequency. As a rule this involves a three-dimensional position and a three-dimensional speed. For applications on the earth's surface using a digital terrain model, a two-dimensional position and a two-dimensional speed, for example, would be determined.
The invention is further described for the three-dimensional case. However, this is not intended to limit the invention to this case.
Exemplary embodiments of the present invention also relate to a system for navigation or position determination, comprising
a plurality of transmitters that emit positioning signals; and
at least one of the aforementioned positioning device according to exemplary embodiments of the present invention.
Exemplary embodiments of the present invention also relate to a radio signal-based positioning method comprising the following steps:
receiving a plurality of radio-transmitted positioning signals;
determining of a frequency of each of the plurality of positioning signals;
determining of a send time of each of the plurality of positioning signals; and
determining of a position location from the determined frequencies and send times of the plurality of positioning signals.
Exemplary embodiments of the present invention also relate to a computer program for carrying out a positioning method according to an embodiment of the present invention, and a computer program product containing a machine-readable program medium on which a computer program according to an embodiment of the present invention is stored in the form of electronically and/or optically readable control signals.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.